Recent studies evidence the interplay between the photosensitivity and the gas sensitivity in porphyrin-functionalized ZnO nanorods. These effects are critically governed by the transport phenomena of electronic charge across the interfaces of organic and inorganic structures. Then the surface potential is a useful quantity to investigate the mutual relationship between these two phenomena. For this scope, Kelvin probe measurements of porphyrin-ZnO structures were performed in the dark, under visible light and exposed to organic vapors. Results show a synergic effect of gas sensitivity and photosensitivity for free base porphyrins, while in the case of metalloporphyrins, the coordinated metal ion alters the cooperation between the two effects, as observed in the Zn complex, where the exposure to light increases the adsorption of gases, but the photovoltage is reduced during the exposure to the gas.